"Eaarth" with a double "a." That's Bill McKibben's moniker for the home that future generations will inherit. A rather cheesy linguistic device, but we get the point: Humans, right now, are in the process of creating a world so different than the one our species grew up with that it might as well be another planet. "We may, with commitment and luck, yet be able to maintain a planet that will sustain some kind of civilization," he writes, "but it won't be the same planet, and hence it can't be the same civilization. The earth that we knew--the only earth that we ever knew--is gone."

What is the nature of double-A Earth? The ice will be thinner, the storms meaner, the ocean more acidic. People will be hungrier. In McKibben's eyes, survival on this altered planet will mean letting go of some cherished notions--especially unrestrained economic growth. Life will become more community-based and less centralized, and perhaps more traditional again. "I'd keep the juice flowing to the Internet even if I had to turn off everything else," he says. But still, the world may stop feeling smaller every day, and start feeling bigger.